1. Field of the Invention
The present invention relates to light source units and display devices, and specifically to cooling light source units.
2. Description of the Related Art
In recent years, for example, as display screens for television sets, computers, etc., flat type display devices such as liquid crystal display devices have been used widely. For example, liquid crystal display devices for transmissive display include a liquid crystal display panel, and a light source unit (also referred to as a backlight unit) disposed on a back surface side of the liquid crystal display panel. Thus, light output from the light source unit is transmitted through the liquid crystal display panel so that desired images are displayed.
For example, in the case of large, liquid-crystal television sets, etc., a so-called direct-backlight structure is often employed for a light source unit. That is, the direct-backlight light source unit includes a reflection sheet and a plurality of light sources disposed in a chassis, and a light diffuser disposed to face the plurality of light sources. Moreover, the light diffuser faces a liquid crystal display panel. On a side of the light diffuser close to the liquid crystal display panel, a plurality of optical sheets is disposed in a stacked manner. It is known that, as the light sources, for example, cold cathode fluorescent lamps (CCFLs), hot cathode fluorescent lamps (HCFLs), light-emitting diodes (LEDs), or the like are used.
When the light source unit is continuously used, heat of the light sources may increase the temperature in the light source unit during use of a display device. The heat may cause faulty operation of electronic circuit components provided in the light source unit, or may change the electro-optical characteristics of liquid crystals of the liquid crystal display panel, which may reduce the reliability of the device.
Thus, it has been conventionally proposed to cool the light source unit by air (for example, see Japanese Patent Publication No. 2006-58679 and Japanese Patent Publication No. H10-106342). Japanese Patent Publication No. 2006-58679 discloses a cooling air passage provided on a further back surface side of a chassis. Moreover, Japanese Patent Publication No. H10-106342 discloses that a reflective plate is disposed on a back surface side of light sources to form an air passage by space between the reflective plate and a chassis.
However, in Japanese Patent Publication No. 2006-58679 and Japanese Patent Publication No. H10-106342, the air passage is provided separately from and independently of spaces in which the light sources are disposed, so that the light sources serving as heat sources cannot be cooled directly. Therefore, it is difficult to increase cooling efficiency of the light source unit.
For example, the luminous efficiency of cold cathode fluorescent tubes or hot cathode fluorescent lamps reaches its peak in a predetermined temperature range, but if the temperature rises above the predetermined temperature range, the luminous efficiency continues lowering. Moreover, the luminous efficiency of LEDs lowers as the temperature rises. Therefore, in order to maintain the luminance of the light source unit, it is very important to appropriately control its temperature rise.